CN 1600279 discloses a localizable medicine releasing device comprising an electronic capsule which consists of a shell, a battery, a remotely controlled module having a miniature heating element, a pre-stressed spring, a piston fixed by a polymer thread, a medicine chamber and a medicine releasing channel. The miniature heating element fuses off the polymer thread when the remotely controlled module receives a control signal. As a result, the piston is allowed to move, under the action of the pre-stressed spring, as to open the medicine releasing channel for releasing the medicine.
The device disclosed in CN 1600279 employs a polymer thread to constrain the piston. Movement of the piston is initiated by fusing the polymer thread via the heating element. Such fusing has the character of a continuous rather than a discrete process. As a result the force with which the polymer thread fixes the piston against movement gradually reduces. Namely, by heating the polymer, which must be a thermoplastic i.e. a thermosoftening plastic rather than a thermosetting plastic, the modulus of elasticity is reduced and consequently the amount of strain in the polymer is increased. Owing to said strain increase the piston is allowed to significantly displace before the polymer thread breaks in two. Therefore the speed with which the piston impacts the medicine is negligible thereby dissipating the contribution of the piston's impulse in releasing the medication from the device. As to compensate such absence of impulse, the spring is required to have a relatively large mechanical stiffness. Said requirement on mechanical stiffness imposes lower bounds 25 on e.g. the spring's coil diameter or compression length thereby increasing the dimensions of the device which is to accommodate said spring. As a result, a problem of the device disclosed in CN 1600279 is in its relatively large dimensions.